As a mechanism to carry information over long distances, store-and-forward (S&F) networks offer an efficient, low-cost alternative to the existing public switched telephone network (PSTN). In general, S&F networks operate parallel to, and are accessed by, the PSTN.
FIG. 1 shows schematically PSTN 30 and S&F network 80 connected in parallel between a source fax machine 10 and a destination fax machine 70. An autodialer 12, positioned between the source fax machine and PSTN 30, designates incoming faxes for transmission over either the PSTN 30 or S&F network 80. If for example the destination of the incoming fax is not one serviced by the S&F network, then the autodialer dials the destination fax number directly to the local exchange 32; the call is then carried in a normal fashion by the PSTN 30 to the destination fax machine 70. In contrast, if the number is one serviced by the S&F network, the autodialer dials the telephone number corresponding to that of the source network node 20. The local exchange 32 then routes the call through the PSTN to the source node. (Note that, depending upon their proximity, the source fax machine 10 and the source network node 20 maybe served by the same or different local exchanges.) Once it has completely received the document, the source node 20 transfers it to the destination network node 40 over dedicated circuit 60. At this point, the destination node 40 dials the destination fax number to its local exchange 36 which in turn transfers the call via the PSTN to the destination fax machine 70. (Note again that, depending upon their proximity, the destination fax machine 70 and the destination network node 40 may be served by the same or different local exchanges.)
In summary, transport of information from the source fax machine to the destination fax machine using the S&F network requires three distinct steps:                (1) from the source fax machine to the source network node via the PSTN;        (2) from the source node to the destination node via dedicated circuits; and        (3) from the destination node to the destination fax machine, again via the PSTN.        
Store-and-forward networks offer a number of significant advantages over standard telephone networks for transport of facsimile. For example, a fax document can be carried 16 times more efficiently using packet technology employed by S&F networks. A common annoyance in telephony is the inability to complete a call, usually because the destination device is busy or does not answer. Although sophisticated voice mail systems have been designed to overcome this problem in voice telephony, similar practical and cost effective solutions do not exist for fax. S&F networks offer a viable solution. A properly implemented S&F network will employ a sufficiently large number of telephone circuits such that a customer fax machine never encounters a busy signal. At the destination end, it is a common practice to design into S&F networks the ability to automatically redial those call attempts which encounter “busy” or “no-answer” signals. Normally, the calls are redialed periodically over a fixed interval of time, every ten minutes for a half hour, for example.
Since multiple messages are typically coursing through an S&F network at any point in time, it is important to have some mechanism to monitor the location and status of each. For example, in one known S&F network, a small data file called an envelope is created to track each fax document as it moves through the network. The source node creates the envelope after it receives an incoming fax document. As the fax document moves through the network, the envelope moves between the network devices and receives continuous updates regarding the status of the fax. This enables substantially real-time monitoring of the fax delivery process.
In the known S&F network, upon concluding the delivery attempt process, the destination network node declares the fax document either “delivered” or “not delivered”; it records the status in the corresponding envelope which is then returned to the source node. If the delivery was successful, the envelope is forwarded to a historical database (HD) which provides a basis for constructing customer bills. If the delivery was not successful, the envelope is forwarded to a delivery assist system (DAS) for further processing. DAS is a database management system which provides a human operator, the document delivery analyst, with the delivery history and options for resubmission to the network of the document in question. One of the possible actions the analyst may take is to assign the fax document to an alternate destination number, i.e., one provided by either the sender or the receiver.
While the delivery analyst (human operator) enables the network provider to arrange delivery of most fax documents, and to provide the customer with an on-going report on alternative delivery attempts, the cost of providing such services are substantial. Furthermore, as the amount of traffic on the network increases, the number of documents requiring assistance increases, and it becomes more and more difficult to provide such human-assisted delivery on a timely and cost-effective basis.
The alternative delivery attempts which the prior art network can make by itself to deliver a document are quite limited. For example, a fax card with hard coded instructions may be provided in each network node which, based on call progress tones heard on the network, may institute an automatic retry. The sounds which may be heard include:                ring, no answer;        busy;        voice.        
Generally, the device automatically retries a number of times in a given time period or cycle, e.g., every five minutes for a half hour, and if delivery is still unsuccessful, the document is transferred to a human analyst.
Thus, the prior art automatic retry device provides a fixed response based on a response received to a first delivery attempt. This system has limited utility and most documents with delivery problems end up being sent to a human analyst. As previously indicated, the cost of providing such human analysts are escalating as the amount of network traffic steadily increases.